1. Field of the Invention
The present invention relates to an evaporator adapted for use in a car air conditioner, and more particularly relates to a stack type evaporator which is improved to first substantially limit the flying of the condensed waterdrops and second to substantially avoid bad odors.
2. Description of the Prior Art
The stack type evaporators of this kind usually comprise plate-like tubular elements each composed of a pair of dish-like core plates 60 as shown in FIG. 11. These core plates face one another and are joined at their peripheries 60a. Such tubular elements are stacked side by side in the direction of thickness, with fin members each being interposed between the adjacent tubular elements. Inlet and outlet header portions 60b and 60c are formed at an end of each tubular element to form a coolant flow path. A coolant flowing through the inlet header portion 60b into the flow path in the tubular element will travel towards another end thereof, and makes one U-turn before coming back into the outlet header portion 60c. These tubular elements thus constitute the "one-sided header" stack type evaporator which is employed widely in this field.
The 37 one-sided header" structure is somewhat disadvantageous in that due to the U-turn which the coolant makes, it cannot flow evenly through the tubular elements but flows in an uneven manner. This will inevitably reduce the effective heat transfer area of each tubular element.
Therefore, another type of evaporator which is of the "both-sided header" structure has been proposed and used in certain cases. This evaporator comprises the tubular elements each having the inlet header portion at its one end and the outlet header portion at its other end.
The prior art stack type evaporators, whether of the one-sided or both-sided structure, employ recessed ribs 70 which are distributed over each core plate 60 as shown in FIG. 11. Those ribs are intended to render turbulent the coolant stream within the tubular elements so as to improve the heat transfer. In detail, many recessed ribs 70 protrude inwardly of two dish-like core plates 60 which are secured one to another at their peripheries to constitute as before each tubular element ( see for example Japanese Utility Model Publication Sho. 56-6847 and ibid. 63-33100).
However, in the use of those stack type evaporators, water which is condensed on the surface of the tubular elements and fin members will stay within the obliquely arranged recessed ribs 70. An angle of contact (hereinafter simply referred to as "contact angle") of each waterdrop with the surface of tubular element or fin member, to which the waterdrop sticks, is so large as to make it difficult for the condensed water to drain smoothly. As a result, the condensed water stays within the air paths, which are each formed between the tubular elements, and through the fin members interposed therebetween, so as to be scattered to fly into the automobile interior compartment to spoil the air-conditioned comfort thereof. Further, the air paths get mildewed due to the adherent condensed water, and a bad smell of mildew or mold will render unpleasant the air stream which flows into the compartment.
In one expedient made to resolve such a problem, the tubular elements and fin members were covered with a hydrophilic surface coating. This coating reduced the contact angle between the surface of tubular element or fin member and the waterdrop. Consequently, the condensed water formed on the surfaces a thin layer which decreased the air flow resistance along the surface, and the thin layer did not stay thereon but was drained smoothly to resolve the problem of flying waterdrop.
A water glass-based coating, as described for example in Japanese Patent Publication Sho. 60-45776, has been preferred as the prior art hydrophilic coating of this kind. A bad smell (like the fishy smell emitted from a hardening cement) inherent in this water glass coating is unpleasant, and spoils the air-conditioned automobile interior into which the air stream flows. Thus, such a prior art coating is not free from the essential problem of bad smell.
A further proposal was made in Japanese Patent Laying-Open Gazette Sho. 62-272099 and also in the U.S. Pat. No. 4,726,886, in order to diminish the bad smell from the hydrophilic coating composed of water glass. The coating in accordance with the further proposal includes silanol, which is a hydrated silicon oxide, and polyvinyl pyrrolidone added thereto. However, because of the silicon oxide-based compound contained therein, this coating also emitted a bad smell similar to that emitted by water glass.
On the other hand, a still further proposal has been made in Japanese Patent Publication Sho. 61-39589 or in Japanese Patent Laying-Open Gazette Hei. 3-49944. This proposal employs a polyamide resin as the component of hydrophilic coating, in place of the water glass compounds (including silanol). Although the unpleasant smell from this resin coating is weaker than that from the water glass coating, the polyamide resin coating still has the following disadvantages. The coating fails to cause the adherent water to form a desirably thin layer which decreases the air flow resistance through the evaporator. Further, the condensed water stays thereon and is not drained smoothly because of the relatively poor hydrophilicity. Thus, the problem of waterdrop flying remains unresolved. Other prior art teachings are Japanese applications 1-299877 and 64-61239 which suggest further variants.
Further, certain of the present applicants proposed in U.S. Pat. No. 5,152,337 giving the tubular elements a revised shape. The tubular elements for a stack type evaporator made of aluminum were designed therein to improve the drainage of condensed water so as to improve heat transfer and to prevent the waterdrop from flying.
According to our earlier proposal mentioned above, each aluminum tubular element is formed with straight drain canals, which extend in parallel with each other from an upper header portion to a lower header portion of the element. The condensed water is guided along the straight canals towards the lower header portion, and then discharged out of the tubular element. Therefore, the condensed water on the surface of each tubular element is removed smoothly through the straight canals.
The stack type evaporator comprising the tubular elements improved in this way has still to be improved in the following ways.
At first, the relatively poor hydrophilicity of the aluminum surface renders it difficult to completely remove the condensed water sticking to and remaining on the surfaces of aluminum tubular elements. Consequently, there is still the possibility that the waterdrop is scattered from the tubular elements.
Second, the tubular elements emit some smells including a metallic smell from aluminum as the base material of the elements, an unpleasant smell from a chemical undercoating which is always formed to enhance corrosion resistance of aluminum article surfaces, and a smell of mildew which grows in the remaining water sticking to the tubular elements.